Mayo Clinic infectious diseases specialist Dr. Pritish Tosh says, "We know there is an association of the Zika virus infection with a certain birth defect, microcephaly, and we are finding out more about exactly what that risk is. It hasn't been defined. If a pregnant woman goes to an endemic area, what are the chances of getting infected, and then, what are the chances of developing microcephaly in their child?"

Dr. Tosh adds, "We are starting to also see new, more rare complications of Zika infection such as Guillain-Barre syndrome and other possible nuerological manifestations."

The CDC also says sexual transmission is much more likely than anticipated. Dr. Tosh says, "The biggest concern remains protecting the woman and her unborn child. It's also important to note that the virus can exist in semen for months after infection. The recommendation is, if a man is infected, that he and his partner wait six months before trying to have a child. If the woman is infected or for the woman who has traveled to endemic areas, the recommendation is eight weeks after travel or infection."

The CDC recommends women in the U.S. defer travel to endemic parts of the world if they are pregnant.